The present invention relates to a leakage diagnosis apparatus and a leakage diagnosis method for a fuel vapor treatment apparatus in an automotive internal combustion engine.
Heretofore, with a fuel vapor treatment apparatus in an internal combustion engine, fuel vapor generated in a fuel tank is introduced to a canister for temporary adsorption, and then the fuel vapor adsorbed in the canister is sucked, together with the new air introduced from a new air introduction opening, through a purge control valve to an intake system of the internal combustion engine. Thereby, the fuel vapor is prevented from being diffused to the outer air (refer for example to Japanese Unexamined Patent Publication No. 5-215020).
According to the above-mentioned apparatus, if a cracking occurs to the piping of a purge line communicating the fuel tank to the purge control valve via the canister, or a sealing error occurs to the joining portion of the piping, the fuel vapor is likely to leak. As a result, diffusion preventing effects can not be sufficiently achieved.
Therefore, as a leakage diagnosis apparatus for diagnosing whether leakage of fuel vapor from the purge line occurs or not, the following method has been proposed.
That is, after the engine is stopped, a drive load (pump operation current value) of an electric air pump utilized as a pressurized air supply device is detected when releasing pressurized air to the atmosphere through a reference orifice having a reference bore, to set a determination level. On the other hand, the drive load (pump operation current value) of the air pump when supplying pressurized air from the air pump to the purge line through the new air introduction opening of the canister is measured as a leak level. The leak level is compared with the determination level, and when the leak level is lower than the determination level, occurrence of leakage is diagnosed.
According to the above method, even when a small amount of leakage occurs through a very fine hole being formed to the piping, the leakage may be diagnosed with high accuracy.
However, the above diagnosis method had drawbacks (1) and (2).
(1) When a large amount of fuel vapor is generated in the fuel tank, due to high fuel temperature inside the fuel tank or large amount of volatile component in the fuel, the pressure rise caused by the fuel vapor is added to the pressure component provided by the air pump. As a result, the pressure inside the fuel tank may exceed the initially expected pressure. This causes excessive load to the fuel tank, which leads to deterioration of endurance of the tank, including fatigue failure.
(2) When a large hole is formed to the fuel tank and the like, the pressurization by the air pump may cause leakage of fuel including the fuel vapor. Further, when a filler cap of the fuel tank is opened during fuel supply to the tank, the pressurization by the air pump may cause fuel vapor to diffuse through an oil filler port.
The present invention aims at solving the above drawbacks. The object of the present invention is to provide a leakage diagnosis apparatus and a leakage diagnosis method for a fuel vapor treatment apparatus, which solves disadvantages caused by the supply of pressurized air during leakage diagnosis.
The present invention relates to a leakage diagnosis apparatus of a fuel vapor treatment apparatus, for diagnosing leakage of fuel vapor from a purge line communicating a fuel tank to a purge control valve via a canister, the fuel vapor treatment apparatus introducing fuel vapor from the fuel tank to the canister having a new air introduction opening for temporarily adsorption, and supplying the fuel vapor adsorbed to the canister, together with the new air introduced from the new air introduction opening through the purge control valve, to an intake system of an internal combustion engine, said leakage diagnosis apparatus comprising a pressurized air supply device for supplying pressurized air to the purge line through the new air introduction opening of the canister while the engine is stopped, a leak level measurement device for measuring a drive load of the pressurized air supply device as a leak level, at a measurement timing after maintaining a pressurized air supply state by the pressurized air supply device for a predetermined time, and a leakage determination device for determining whether leakage occurs or not based on the leak level.
Here the present invention is characterized in that the above leakage diagnosis apparatus includes a pressurized air supply ceasing device for ceasing an operation of the pressurized air supply device when the drive load of the pressurized air supply device is not within a predetermined range.
When the drawback explained in (1) occurs, the drive load of the pressurized air supply device exceeds an upper limit side predetermined value. When the drawback explained in (2) occurs, the drive load of the pressurized air supply device becomes smaller than a lower limit side predetermined value. Therefore, according to the invention, the supply of pressurized air is ceased when the drive load is not within the predetermined range.
Accordingly, in a case where a large amount of fuel vapor is generated in the fuel tank and the pressure rise caused by the fuel vapor is added to the pressure component provided by the pressurized air supply device so that the pressure inside the fuel tank may exceed the initially expected pressure, the drive load of the pressurized air supply device is detected to have reached the upper limit side predetermined value or above, and the operation of the pressurized air supply device is ceased. Thereby, deterioration of endurance, including fatigue failure, of the fuel tank caused by excessive load can be prevented.
Further, when a large hole is formed to the fuel tank, the pressurization provided by the pressurized air supply device may cause leakage of fuel including fuel vapor. Moreover, when a filler cap of the fuel tank is opened during fuel supply to the fuel tank, the pressurization may cause fuel vapor to diffuse through the oil filler port. In such cases, the drive load of the pressurized air supply device is detected to have reached the lower limit side predetermined value or less, and the operation of the pressurized air supply device is ceased. Thereby, fuel is prevented from leaking.
Moreover, the present invention includes a warning device which, when the operation of the pressurized air supply device is ceased, provides a warning of such state.
Preferably, the warning device separates the state where the drive load is equal to or above the upper limit side predetermined value from the state where the drive load is equal to or below the lower limit side predetermined value, to provide a warning, for the upper limit side predetermined value and the lower limit side predetermined value which define the predetermined range. Thereby, the rising of inner pressure of the tank may be separated from the fuel leakage, to be warned
Further, the present invention includes a determination level setting device for detecting the drive load of the pressurized air supply device when the pressurized air from the pressurized air supply device is released to the atmosphere through a reference orifice having a reference bore, to set a determination level. The leak level is compared with the determination level by the leakage determination device to determine whether leakage occurs or not. Thereby, the accuracy of leakage diagnosis is improved.
In a case of such a determination level, the predetermined range may be set based on the determination level, so as to determine more precisely whether to perform the pressurization or not.
Further, according to the present invention, the pressurized air supply device is an electric air pump, and the drive load of the pump is detected through a pump operation current value. This enables easy and accurate leakage diagnosis or determination on whether or not to perform the pressurization, without the need to add a pressure sensor and the like.
These and other objects and phases of the present invention will become apparent from the following explanations disclosing the preferred embodiments of the invention with reference to the accompanied drawings.